This Application is a 371 of PCT/HU96100077, filed Dec. 16, 1996 which is based on Hungarian Application P9603093, filed Nov. 08, 1996.
The invention relates to a new catalyst applicable in hydrocracking of hydrocarbons. More particularly, the invention relates to a catalyst comprising as active components ZSM-5 zeolite which has been subjected to ion exchange with nickel and magadiite in hydrogen form (further on: Ni-ZSM-5/H-magadiite catalyst). This catalyst can be applied to particular advantage in hydrodewaxing of gas oil, and possesses high selectivity and a long life time.
The invention also relates to a method for producing arctic gas oil (i.e. gas oil with extremely low pour point) by subjecting gas oil to hydrodewaxing in the presence of the above catalyst.
It has been known for a long time that pour point of gas oils can be lowered by reducing the amount of higher straight-chained and moderately branched--with only single methyl groups in side chains--paraffins (further on: n-paraffins) contained therein. One of the methods suitable for reducing the amount of n-paraffins in gas oils is cracking in the presence of hydrogen and a catalyst, i.e. catalytic hydrocracking (hydrodewaxing) of gas oils. For this purpose, those catalysts (so-called shape-selective catalysts) are particularly suitable which catalyse only the cracking of higher n-paraffins intended to be removed, but do not or only slightly catalyse the cracking of other components (such as isoparaffins, lower hydrocarbons, etc ). Such shape-selective catalysts have been disclosed, inter alia, in U.S. Pat. Nos. 3,700,585 and 3,894,934. A very widely used representative of shape-selective catalysts is the commercially available ZSM-5 zeolite catalyst in hydrogen form (ZSM-5 or, according to a more accurate terminology, H-ZSM-5) Utilizing such catalysts, pour point of gas oils can be lowered typically to -5 to -25.degree. C., depending on the pour point of the starting substance. Hydrogen gas present at cracking does not participate in the reaction, and its role is only to suppress further dehydrogenation of olefins with a single unsaturated bond, which are one of the primary products of cracking This further dehydrogenation of olefins proceeds upon thermal effects, and leads to coke-formation on the catalyst, decreasing (in extreme cases even breaking down) thereby the activity of the catalyst. It is, however, obvious that further dehydrogenation of olefins with a single unsaturated bond can be suppressed only to an extent determined by the reaction equilibria under the prevailing conditions and by the law of mass action.
A smaller fraction of olefins with a single unsaturated bond, which form as primary products in hydrocacking, consists of lower hydrocarbons which appear in gasoline (a twin product of hydrocracking). These compounds have a favourable influence on the quality of gasoline However, the situation is different with higher olefins having a single unsaturated bond which appear in gas oil. Hydrogen present in the process only suppresses but does not prevent the thermal dehydrogenation of these latter olefins. A part of the resulting olefins with multiple unsaturated bonds adsorbs on the surface of the catalyst and gets coked there, whereas another part of them gets stabilized by conversion into aromatics. The resulting aromatics decrease the cetane number of gas oil and lead to an increase in noise level when gas oil is used in engines.
A method for suppressing these latter disadvantages has been disclosed in Hungarian Patent No. 209,141. According to this method, gas oil is subjected to hydrodewaxing in the presence of a catalyst comprising as active components ZSM-5 zeolite which has been subjected to ion exchange with nickel, and magadiite which has been subjected to ion exchange with nickel (Ni-ZSM-5/Ni-magadiite catalyst). This catalyst is able to suppress the formation of aromatics from olefins with multiple unsaturated bonds, whereby both the decrease in cetane number and the increase in noise level upon use in engines can be suppressed considerably, without affecting, however, the level of n-paraffin removal and thereby the pour point of the resulting gas oil.
However, with the increase of motorisation, there is an increasing need for gas oils with extremely low pour point, typically about or below -50.degree. C., the production of which has not yet been solved.